1. Field of the Invention
The invention relates to a self-propelled construction machine, in particular a road milling machine, which possesses an undercarriage which has front and rear—in the working direction—wheels or travelling gears, a machine frame which is borne by the undercarriage and a working means. Furthermore, the invention relates to a method for controlling a self-propelled construction machine, in particular a road milling machine.
2. Description of the Prior Art
Various types of self-propelled construction machine are known. These machines include for example the known road milling machines or slipform pavers. These construction machines are distinguished in that they possess a working means for altering the ground or for constructing structures on the ground. In the known road millers, the working means has a milling drum equipped with milling implements, with which material can be milled off from the road surface in a specified working region.
When planning and executing a construction project which is to be carried out with the known road milling machines, the problem arises that objects already present in the ground, for example manhole covers, storm drains or hydrants, have to be taken into account. The region of the ground in which for example a manhole cover lies should not be altered using the road miller, since the manhole cover and the road miller might otherwise be damaged.
In order to take into account objects present in the ground, it is necessary to intervene in the machine control. The milling drum of a road milling machine, for example when travelling over a manhole cover, has to be raised out of a specified position in relation to the surface which is to be altered taking into account a safety distance within a specified stretch or distance, which is dependent on the dimensions of the manhole cover. The operator of the machine cannot, however, recognise the exact position of the manhole cover level with the milling drum in practice, since the milling drum is located beneath the driving position. Therefore the position of a manhole cover in the ground in practice is marked with lateral lines which can be recognised by the operator of the machine or another person. However, it proves disadvantageous in practice to mark objects which are present in the ground. First of all, to mark the objects requires an additional working step. Furthermore, it is difficult to draw the lines exactly at a right-angle to the direction of travel. Further, the lines cannot be recognised, or can be recognised only with difficulty, when it is dark. Moreover, it is not readily possible to mark the objects if it is raining. Because of the inaccuracies, it is therefore necessary to select a relatively large safety distance, which makes a greater amount of subsequent work necessary.
The use of a display unit to simplify handling of a construction machine is known from DE 10 2010 048 185 A1 (U.S. Pat. No. 8,977,442). DE 10 2010 048 185 A1 however describes a means for facilitating the maneuvering of a construction machine on the ground, which means uses sensors to detect the steering angle of the travelling gears which has been set by the operator of the machine. Trajectories which describe the path of travel of the construction machine are displayed for the operator of the machine on the display unit.
US 2009/0016818 A1 and US 2012/0001638 A1 describe construction machines which possess a means for recognising metallic objects which may lie beneath the ground surface. If a metal object is recognised, the road milling machine can be stopped or the milling drum can be raised. The objects concealed in the ground can be recognised using a metal detector.